The first results achieved in the French ANR (National Research Agency) project BANET (Body Area NEtwork and Technologies) are presented (Part I). This project mainly deals with the antenna design in the context of Body Area Networks applications and channel characterization. General conclusions are drawn on the body impact on the antenna performance for on-on and in-on communications (Medical Implant Communication Systems). Narrow-band and ultra-wideband contexts are addressed both numerically and experimentally, and it is shown that design questions are significantly different for each case, leading to different constraints and guidelines. For narrow-band antennas, an alternative and original approach of desensitization using ferrite sheets is proposed and compared to classical techniques based on ground-plane screening. The characterization of numerical phantoms is also analyzed with narrow-band canonical antennas. For the specific on-on scenario, morphologies and electrical properties of the human tissues are also included in the topics of interest. For ultra-wideband antennas, focus is put on planar balanced designs, notably to reduce harmful "cable effects" occurring during the antenna characterization or the channel sounding. For both types of antennas, the main parameter under study is the distance to the body, which has a significant influence.